System for delivering and vaporizing liquid at a continuous and constant volumetric rate and pressure

ABSTRACT

An improved vaporization system includes an automated valve and positive displacement pumping system using a pair of pumps operating in opposition to one another to provide continuous and constant volumetric flow at a constant predetermined pressure to an improved vaporizer using a stack of heated disks to flash vaporize the liquid. The valves are improved by providing one way flow.

The present invention relates to liquid pumps and vaporizers, and moreparticularly to an improved liquid delivery and vaporization systemincluding a novel positive displacement pump assembly for delivering acontinuous volume flow at a constant rate to an improved vaporizerassembly for flash vaporizing the liquid.

Many processes are known where corrosive, sometimes pyrophoric, liquidmaterials must be vaporized so that the gas vapors can be subsequentlyused in carefully controlled amounts in a process chamber as a part of acarefully environmentally controlled process. Because of the toxic anddangerous nature of these materials, systems for delivering the liquidsto the vaporizer, as well as the vaporizer itself, must be carefullysealed to prevent the escape of the materials. Various such systems areknown. One type of system automatically fills the liquid into a bottle.The bottle is heated in order to increase the vapor pressure in thebottle up to a sufficient pressure so that a thermal mass or pressurebased flow meter can be used to measure and control the flow of the gas.In some of these systems inert gas is also bubbled through the liquid inorder to help carry off more vapor. Such systems tend to be relativelyexpensive and cumbersome, with vapor flow lines requiring extensiveheating to prevent condensation.

It is a principal object of the present invention to provide an improvedliquid delivery vaporization system which overcomes, or substantiallyreduces the problems of the above-noted prior art.

A more specific object of the present invention is to provide animproved relatively simple and inexpensive liquid delivery andvaporization system adapted to be mounted directly on the processingchamber requiring few, if any, vapor flow lines.

Another object of the present invention is to provide an improvedvaporizer for vaporizing a liquid in an energy efficient manner, withminimal atomization, and without the need for additional inert gases.

And another object of the present invention is to provide an improvedpositive displacement pumping system for delivering liquid to avaporizer at a continuous constant volumetric flow rate and subtantiallyindependent of downstream pressure.

And yet another object of the present invention is to provide animproved pump assembly for pumping liquid at a continuous, constantvolumetic rate with minimal parts exposed to the liquid passing throughthe pump.

And still another object of the present invention is to provide animproved valve for allowing flow to occur only in one direction when athreshold pressure at the inlet of the valve has been achieved.

In accordance with one aspect of the present invention these and otherobjects of the present invention are achieved by an improved vaporizercomprising a plurality of relatively thin disks supported in a stack andheated above the vaporization temperature of the liquid so that whenliquid is forced between adjacent surfaces of the disks the liquid flashvaporizes with little atomization.

In accordance with another aspect of the present invention an improvedvalve system is provided. The valve system comprises means for biasing avalve body closed on a valve seat with sufficient force so that thevalve will open in response to a predetermined pressure at its inlet,but will not open in response to the predetermined pressure when exertedas back pressure on the valve body while the valve system is closed.Means are also provided for independently exerting a force opposite thebiasing force so that the valve can be opened.

In accordance with another aspect of the present invention an improvedpump is provided. The pump pumps fluid at a continuous and constantvolumetric rate. The pump comprises means for varying the volume of thepump chamber so that the pump can be filled and liquid subsequentlydelivered. The means for varying the volume of the pump chamber includesa compartment filled with a substantially incompressible fluid, such asoil. The compartment and chamber are separated by means for decreasingthe volume of the chamber when the actuating means applies pressure tothe incompressible liquid so as to provide positive pressure toward theoutlet, and increasing the volume of the chamber when the actuatingmeans withdraws pressure from the incompressible liquid so as to providenegative pressure relative to the inlet so as to fill the chamber.

Finally, in accordance with yet another aspect of the present inventionan improved positive displacement pump assembly is provided for pumpingfluid at a continuous, predetermined volumetric rate. The assemblyincludes control means for cyclically operating a first pumping means(shown and described in FIG. 1 as P_(X1)) connected between a first andsecond valve means (shown and described in FIG. 1 as V₁ and V₂,respectively) and second pumping means (shown and described in FIG. 1 asP_(X2)) connected between the second and a third valve means (shown anddescribed in FIG. 1 as V₂ and V₃, respectively) as follows:

(a) with the first valve means (V₁) open and the second valve means (V₂)closed, operating the second pump means (P_(X2)) in its delivery phaseso as to pump fluid in the chamber of the second pumping means (P_(X2))through the third valve means (V₃), and operating the first pump means(P_(X1)) in its filling phase so as to fill the chamber of the firstpumping means with fluid passing through the first valve means (V₁) at avolumetric rate greater than the predetermined rate so that the chamberof the first pump means (P_(X1)) is filled prior to the completion ofthe delivery phase of the second pump means (P_(X2));

(b) closing the first valve means (V₁) while maintaining the secondvalve means (V₂) closed when the chamber of the first pump means(P_(X1)) is filled;

(c) commencing the first pump means (P_(X1)) in the delivery phase whilemaintaining the first and second valve means closed (V₁, V₂) so thatwhen the fluid in the first pump means (P_(X1)) reaches a predeterminedpressure (i) the second valve means (V₂) opens and the third valve means(V₃) remains open, (ii) the second pump means (P_(X2)) commences itsfilling phase, and (iii) the first pump means (P_(X1)) continuesoperating in its delivery phase so that the volume of fluid deliveredfrom the chamber of the first pump means (P_(X1)) to the chamber of thesecond pump means (P_(X2)) while the latter is filling results in fluidpassing though the third valve means (V₃) at the predeterminedvolumetric rate.

Other objects of the invention will in part be obvious and will in partappear hereinafter. The invention accordingly comprises the apparatuspossessing the construction, combination of elements and arrangement ofparts which are exemplified in the following detailed disclosure, andthe scope of the application of which will be indicated in the claims.

For a fuller understanding of the nature and objects of the presentinvention, reference should be had to the following detailed descriptiontaken in connection with the accompanying drawings, wherein:

FIG. 1 is a schematic diagram generally illustating the preferreddelivery and vaporization system of the present invention;

FIG. 2 is a schematic illustration taken in longitudinal cross sectionthrough the preferred embodiment of the pump as designed and used inaccordance with the present invention;

FIG. 3 is a schematic illustration taken in longitudinal cross sectionthrough the preferred embodiment of each of the valves V₁ -V₄ of FIG. 1as designed and used in accordance with the present invention;

FIG. 4 is a schematic illustration taken in longitudinal cross sectionthrough the preferred embodiment of the vaporizer as designed and usedin accordance with the present invention;

FIG. 5 is a longitudinal cross sectional view of the preferredembodiment of the pump assembly shown generally in FIG. 1;

FIG. 6 is an enlarged more detailed longitudinal cross-sectional view,partially cut away, of the pump and valve shown in FIG. 5;

FIG. 7 is a longitudinal cross sectional view of the preferredembodiment of the vaporizer shown generally in FIG. 1; and

FIG. 8 is a flow chart illustrating the operation of the controller forsequencing the components of the vaporization system of the presentinvention.

In the drawings the same numbers are used to referred to the same orsimilar parts, and the same number with letters designating identicalparts.

Referring to FIG. 1, the vaporization system of the present invention,generally shown at 20, comprises a pump assembly 22 having its inletconnected to a reservoir 24, the latter preferably being pressurized.The liquid provided by reservior 24 to the assembly 22 can be controlledwith the valve 25 separately operated by the operator. Pump assembly 22is a positive displacement pump adapted to continuously pump liquid at aconstant volumetric rate. The pump assembly has a first valve V₁ havingan inlet connected to receive liquid from the reservoir 24 and an outletconnected to the inlet of a first pump P_(X1). The outlet of the pumpP_(X1) is connected to the inlet of valve V₂, which in turn has itsoutlet connected to the inlet of pump P_(X2). The latter has its outletconnected to the inlet of valve V₃. The outlet of valve V₃ forms theoutlet of the pump assembly 22. A fourth valve V₄ has its inletconnected to the outlet of valve V₃ and its outlet connected to theinlet of valve V₁ and is used when the pump assembly operates in arecirculating mode. As will be described in greater detail hereinafter,the valves V₁, V₂, V₃ and V₄ are each designed as "one way" valves sothat, if closed, they will not open in response to back pressure.

The system 20 also includes a vaporizer assembly 26 having a vaporizer28, the latter having its inlet connected to the outlet of the pumpassembly 22 (i.e., the outlet of the valve V₃) so as to receive theliquid output of the pump assembly. Valve 25a and its downstream pipingare used for pump and vaporizer evacuation such that the entire systemmay be liquid-filled without trapped gases. As will be evidenthereinafter the the vaporizer 28 has two outlets, one for connecting thevaporizer gas output to a first valve V₆ of the assembly 26, the valvein turn being connected to the vacuum pump 30. The output of pump 30 ispreferably connected to a closed system (not shown) for capturing theoutput of the vacuum pump when the latter is used. The other outlet ofvaporizer 28 is connected to a second valve V₅ of the assembly 26, thelatter valve being connected to a system 32, such as a processingchamber (not shown).

As will be more evident hereinafter, the vaporization system includes acontroller 36 for controlling the sequencing and operation of the pumpsP_(X1) and P_(X2) and valves V₁ -V₆ of the pump assembly 22 andvaporizer assembly 26. The controller preferably includes amicroprocessor preferably programmed so as to operate the pumps andvalves in accordace with a predetermined and novel sequence, all ofwhich will be more evident hereinafter. In addition the preferred valvesV₁ -V₆ are pneumatically actuated and therefore are connected to asource 34 of pressurized air, each through a correspondingelectromechanical valve 38a-38f. The opening and closing of the latteralso is controlled by the controller 34. As will be more apparenthereinafter, the pumps P_(X1) and P_(X2) and the valves V₁ -V₄ areconstructed in a novel manner.

The pumps P_(X1) and P_(X2) are substantially identical, except as notedbelow, with a simplified schematic longitudinal cross sectional view ofone of the pumps being shown in FIG. 2. As shown in FIG. 2, the inlet 52and outlet 54 of each pump P are connected to the associated valves,indicated at 56 and 58, respectively. The pump includes a pump chamber60 having a volume which changes as the pump fills and delivers. Thechamber in turn connects the inlet to the outlet so that when the valves56 and 58 are opened, liquid will pass through inlet 52 into the chamber60, and subsequently through outlet 54. The pump P also includes acompartment 62 separated from the chamber 60 by an expandable bellowsseal 64. It should be evident that other expandable elements, such as adiaphragm or a bellowfram can be used in place of the seal 64. Thecompartment 62 is filled with a substantially incompressible liquid,e.g., oil. Actuating means, shown in the form of a ram shaft 66, ismovable through the seal 68 into and out of the compartment 62. Theshaft preferably has a uniform cross sectional area along its length sothat as the shaft 66 moves into or out of a tubular fitting 67 disposedwithin the compartment at a uniform rate, the displaced oil willrespectively cause the bellows seal to expand or contract at a uniformrate resulting in the volume within the chamber increasing or decreasingat a uniform rate.

More specifically, during the filing phase of each pump, the shaft 66retracts from the compartment 62 (and therefore causes the bellows seal64 to contract) at a uniform rate. During this phase the valve 56 isopened in order to allow liquid to pass through the inlet 52 into thecompartment 62. The volume of the chamber 60 enlarges at a uniform rateas the ram shaft retracts. During the delivery phase of the pump, theshaft 66 is movable in the opposite direction (in an upward direction inFIG. 2) so that the shaft moves into the compartment (and thereforecauses the bellows seal to expand). As will be more evident hereinafter,during the delivery phase, the valve 58 may be initially closed so thatany back lash in the system can be accounted for and the pressure of theliquid in chamber 60 increased to a predetermined level, before valve 58is automatically opened in response to the increasing pressure at theinlet. The cross-section of each of the inlets and outlets 52 and 54 areof a relatively small dimension (e.g., 1/32nd or 1/16th of an inch) forreasons which will be described in greater detail hereinafter.

The valves V₁ -V₄ are also indentical to one another, with a simplifiedcross sectional view of one of the valves V being shown in FIG. 3. Eachvalve V includes an inlet 72 to and outlet 74 from the valve passageway76. Both the inlet and outlet are of a relatively small cross-sectionaldimension, and in the preferred embodiment are merely extensions of theinlets and outlets 52 and 54 of the associated pump as best seen inFIGS. 5 and 6 described hereinafter. A valve seat 78 is provided withinthe passageway 76 at the outlet 74. A valve body 80 is movable withinthe passageway relative to the valve seat between an opened positionwherein the end of the valve body (shown as a spherical ball 82) isspaced from the valve seat 78, and a closed position when the body 80,and in particular the ball 82, is in contact and seals with the seat.Means for moving the valve body 80 (and spherical ball 82) between theopened and closed position includes a piston 84 including a piston head86 in contact with the valve body 80, a shaft 88, mounted for axialmovement toward and away from the valve seat 78, for moving the valvebody toward the valve seat and a pneumatic actuator head 90 for axiallymoving the shaft. The actuator head is disposed within an air chamber 92so that it can move in the same axial direction as the valve body 80 andshaft 88 O-ring 91 provides a seal between head 90 and the wall ofchamber 92. Means, in the form of one or more compression springs 94,bias the actuator head 90, shaft 88, piston head 86 and valve body 80into the closed position. A flexible bellows seal 96 separates theliquid in valve passageway 76 from the actuating portion of the valveassembly. The force provided by the compression spring 94 is sufficientto maintain the valve closed until the pressure of the liquid in thebellow seal 96 exceeds a predetermined pressure due to the forcesexerted by the liquid side of the bellows seal in contact with thebottom of the piston head 86. In the preferred embodiment of the valveassembly, the valve assembly is designed to automatically open when thepredetermined pressure of the liquid in the passageway 76 of the valveassembly reasches 250 psi, although this design threshold pressure canvary. Further, because of the relatively small cross-sectional dimensionof the outlet 74, when the valve assembly is closed and the backpressure of the liquid in outlet 74 reaches the threshold level theforce exerted on the ball 82 is insufficient to open the valve due tothe much smaller area upon which force is applied (compared to the areaof the bellows seal in contact with the bottom of the piston head 86).An air line 97 is connected to the air chamber 92. When pressurized airis introduced through air line 97 into the chamber 92, sufficient forceis applied to the actuator head 90 so as to move the head 90 axiallyagainst the bias of the compression spring 94 moving the shaft 88 andvalve body 80 away from the valve seat 78 to the opened position. TheO-ring seal 98 maintains the air chamber 92 air tight. Finally, ifnecessary a compression spring 99 can be provided to insure that thebody 80 unseats from the valve seat 78 when the valve is opened.

The simplified longitudinal cross sectional view of the vaporizer 28 isshown in FIG. 4. Vaporizer 28 includes a heater assembly 100 including ablock 102 and heater elements 104 inserted in the block 102 so as toform a heat source for the stack of disks 106. The disks are preferablyflat and annular in shape and very thin and secured in the absence ofliquid flow in contact with one another so that good heat conduction isprovided from the block 102 through the disks 106 and the surface areaof each of the disks can be heated above the flash point of the liquidbeing pumped into the vaporizer. The disks, for example, can have adiameter to thickness ratio of 1 inch: 0.001 inch, although thedimensions and ratio can vary. A center aperture is formed in the heaterblock and aligned with the center apertures of the disks so that a smalltube 108 can be positioned through the block and disks. The tube 108 isprovided with a plurality of apertures 109 around its circumferenceadjacent the internal rim of the disks so that liquid (indicated as L inFIG. 4) forced through the tube will be forced between the disks 106. Tobias the disks together, while insuring the passage of liquid betweenthe disks, an anvil 110 is biased, with for example one or morecompression springs 112, into contact with the stack so as to force thedisks of the stack into contact with one another and the heater block.The disks 106, anvil 110, springs 112 and the portion of the tube 108extending through the heater block into the disks are all containedwithin a vaporization chamber 114 having the vapor outlet 116. As liquidis forced through the tube 108, it will force the disks apart againstthe bias of springs 112 so that liquid will be forced between adjacentdisks. The large confronting surface areas of the disks provide largehot surface areas which heat the relatively thin layers of liquidtherebetween above the flash point so that the liquid is flash vaporizedand passed as vapor out of the outlet 116.

A more detailed illustation of the pump assembly is shown in FIGS. 5 and6. Three blocks 130a, 130b and 130c respectively are provided fordefining the inlets 72 and outlets 74 of the valves V₁, V₂ and V₃. ValveV₄ is secured to the bottom of the block 130c. Valves V₁, V₂ and V₃ arerespectively secured to the top of each block. The outlet 74 of valve V₁forms the inlet 52 of the pump P_(X1), while the outlet 74 of valve V₂forms the inlet 52 of the pump P_(X2). The blocks 130 are secured withgaskets 132 so that the outlet 54 of block 130b is connected to theinlet 72 of block 130a, and similarly outlet 54 of block 130a isconnected to the inlet 72 of block 130c. The bottom of each of theblocks 130a and 130b is counterbored so as to form the space for chamber60 and compartment 62.

The pumps P_(X1) and P_(X2) are respectively connected with any suitablemeans such as plates 136 and screws 134 to the bottom of the respectiveblocks 130a and 130b. The open end of bellows seal 64 is secured betweenthe bottom of the respective block and plate so as to separate the oilchamber 62 from the liquid passageway 60. Each plate includes a centeraperture which is counter bored so as to provide an annular shoulder forsupporting the O-ring seal 68. Each plate 136 supports a housing 138,which in turn supports the pumping actuator mechanism.

Specifically, a stepping motor 140 drives a shaft 142 of ball nutassembly 144 through the coupler 146. A rotation to linear motiontranslating element 148 for supporting the ram shaft 66a or 66b issecured to the nut assembly 144 and slidable on the anti-rotation shafts150 so that rotation of the stepping motor causes the shaft 142 of theball nut assembly 144 to rotate. This, in turn, causes the element 148to slide on the shafts 150 so that the ram shaft 66 can be moved withinthe O-ring seal 68 in and out of the oil in the compartment 62 dependingon the direction of rotation of the motor 140.

Thus, by causing the stepping motor 140 to rotate in one direction at aconstant angular speed, the shaft 66 will move into the compartment at aconstant linear speed. Similarly, by reversing the direction of themotor and rotating the shaft 142 of the nut assembly at a constantangular speed in the opposite direction, the shaft 66 will retract fromthe chamber at a constant linear speed. For reasons which will be moreevident hereinafter, the ram shaft 66b of the pump P_(X1) has a crosssectional area twice that of the ram shaft 66a of the pump P_(X2) sothat for a given angular speed at which the motors 140 are driven, theram shafts are driven into the corresponding compartment 62 at the samelinear speed resulting in the ram shaft 66b displacing twice the amountof liquid in the chamber 60 of the block 130b than the ram shaft 66adisplaces in the chamber 60 of the block 130a. As shown the onlyportions of the pump assembly exposed to the toxic and dangerous liquidis the block 130, bellows seal 64 and gasket 132. As such these elementsare made of a material non-reactive with the liquid passing through thepump. For example, for most applications, these parts can be made of astainless steel, although other materials are also available.

The valves V₁ -V₄ are all identical, with the details of the preferredvalve being shown best in FIG. 6. Each valve is secured to a block 130and includes a main block element 160 having a center bore for receivingthe piston shaft 88. The main block element 160 is provided on itsbottom surface with a cylindrical extension 162 within which a counterbore receives the bellows seal 96 and spring 99 and is in fluidcommunication with the inlet 72 and outlet 74 so as to define thepassageway 76. The extension 162 is adapted to mate with a dimple formedin the top of the corresponding body 130 so as to insure that the valveis properly seated. The valve body 80 and ball 82 are disposed withinthe bellows 96 and are movable up and down (as shown in FIG. 6) betweenan opened and closed position, while the compression spring 99 isdisposed within the bellows seal so as to insure the valve body unseatsfrom the valve seat when the valve is opened. The top of the main blockelement 160 is also counter-bored to receive the O-ring seal 98, andfurther counterbored at 163 on the top of the element so that thecounterbore and cover plate 164, secured over the counterbore 163, formthe air chamber 92. The O-ring 98 is provided on an annular shoulderformed in the main block element, while wells are formed in the plate164 for receiving a plurality of compression springs 94. An air inlet 97is formed in the main block element 160 so that air is forced into thechamber 92 forcing the actuator head 90, in an upward direction as shownin FIG. 6. Again the parts of the valve exposed to the liquid, i.e., thevalve body 80, ball 82, bellows seal 96 and main block element 160 areall made of a material non-reactive with the liquid passing through thevalve.

Finally, the vaporizer assembly 26 is shown in greater detail in FIG. 7.As shown, cap 170 is secured over the heating block 102 with a sealinggasket 172 so as to cover the disks 106 and anvil 110. The heating block102 is provided with two valve seats 174 for receiving the valve body ofthe corresponding valves V₅ and V₆. The valves V₅ and V₆ are pneumaticvalves and move the respective valve bodies 176 into and out of contactwith the respective seats 174.

The operation of the entire vaporization system 20 will now bedescribed. As shown in FIG. 8 the controller operates the pumping system22 in accordance with a predetermined sequencing so as to provide aconstant volumetric rate of flow of liquid at the output of the pumpassembly to the vaporizer 28. More specifically, in FIG. 8 during startup, as indicated at step 200 valves V₁, V₂, V₃, V₄, V₆ and 25a areinitially opened so that air will be removed from the pumps, vaporizerand interconnecting lines by vacuum pump 30. When the pressure has beenreduced to substantially zero (e.g., <50 milliTorr) valves V₆ and 25aare closed and valve 25 is opened allowing liquid to flow from thereservoir filling all evacuated spaces right up to the vaporizer disks106 of vaporizer 28. Pumping and vaporizing can now begin.

The controller proceeds to step 202 at the beginning of its operationalcycle and will shut off the valve V₆ by closing the valve 38f, thestepping motor 140 and the ram shaft 66 of the pump P_(X2) will be atthe beginning of the delivery phase of that pump, so that the ram shaftis fully retracted from the oil chamber. The stepping motor 140 and ramshaft 66 of pump P_(X1) will be at the beginning of the filling phase ofthat pump, so that the ram shaft will be fully extended into the oilchamber. At step 202 valve V₃ remains opened, V₄ remains closed, whilevalve V₅ is now opened (by opening valve 38e) and valve V₆ is closed sothat vapor from the vaporizer assembly 26 will be diverted to the system32. In addition, at step 202, valve V₂ is closed. During each cycle thepumps operate in opposition to one another so that the pump P_(X2) nowbegins to deliver liquid at a constant volumetric rate through the valveV.sub. 3 which opens automatically when the liquid pressure generated bypump P_(X2) reaches the level to overcome the spring force on top of theair piston (in the preferred example, 250 psi). Simultaneously, thestepping motor of pump P_(X1) begins its filling phase by operating attwice the speed of the stepping motor 140 of pump P_(X2) during thelatter's delivery phase so that the position of the ram shaft of pumpP_(X1) is at its nominal starting position halfway through the deliveryphase of pump P_(X2). The ram shaft is allowed to retract slightlyfurther (e.g., typically an extra fifteen steps of the stepping motorout of a total 800 steps taken during the complete delivery phase) andstops at step 204. The delivery phase of pump P_(X2) continues untiljust before the delivery phase of that pump ends (in the example given,with 15 steps of the motor 140 of the pump P_(X2) being left beforecompletion of the delivery phase).

At step 206 valve V₁ is pneumatically closed by closing valve 38a, themotor 140 of pump P_(X1) reverses and that pump begins its deliveryphase with the valve V₂ remaining closed until the ram shaft 66 reachesthe nominal starting position (in the example given, for the firstfifteen steps of the motor). This enables the pump P_(X1) to accommodateany mechanical backlash in the ball nut assembly of the pump P_(X1) andto compress the oil and liquid, to the extent they are compressible, inthe chamber and passageway of the pump. At this point the pressure inthe inlet of valve V₂ will be at the threshold level 250 psi.

Thus, at step 208, upon completion of the delivery phase of pump P_(X2),pump P_(X1) is now ready to deliver liquid at a constant volumetric rateand predetermined pressure. At step 208 valve V₂ opens automatically dueto the pressure upstream caused by pump P_(X1). Pump P_(X1) willcontinue its delivery phase with valve V₂ opening automatically, andpump P_(X2) will begin its filling phase. Because pump P_(X1) deliverstwice the volumetric rate as pump P_(X1), pump P_(X1) will deliverenough liquid to simultaneous fill pump P_(X2) and deliver liquid out ofvalve V₃ at the same volumetric rate as was delivered by pump P_(X2).

Once pump P_(X1) has completed its delivery phase at step 210 ofoperation, the process repeats with valve V₁ opening, closing valve V₂due to the sudden drop in pressure because V₁ was pneumatically opened.The pump P_(X2) begins its delivery phase and pump PX1 begins itsfilling phase at twice the speed of pump P_(X2), all by repeating step202 and then subsequently repeating steps 204-210.

It should be appreciated that as the liquid is pumped through thevaporizer 28 by the pumps P_(X1) and P_(X2), the liquid is flashvaporized and forced by pressure through valve V₅ to the system 32.

As shown in FIG. 8 if it is desired to temporarily stop the process atthe end of step 210, the pump assembly can be operated in arecirculation mode, simply by opening valve V₄ by opening valve 38d toallow the output flow of liquid from valve V₃ to flow back to the inputof valve V₁.

During the operational mode and recirculation mode, the stepping motors140 of the pumps operate continuously, first in one direction for thefilling phase, and then in the other direction for the delivery phase,with the reversing of direction from one phase to the other occuringalmost instantaneously.

The system 20 thus described provides an improved relatively simple andinexpensive vaporization system adapted to be mounted directly on thevapor processing chamber requiring few short vapor flow lines. Theimproved vaporizer 28 vaporizes liquid in an energy efficient mannerwith minimal atomization, and without the need for additional inertgases. The pumping assembly 22 provides and improved positivedisplacement pumping system for delivering liquid to a vaporizer at aconstant volumetric rate. The pumps P_(X1) and P_(X2) each provide animproved pump for providing a constant volumetric rate and pressuredelivery when operating in a delivery phase with minimal parts exposedto the liquid passing through the pump. Each valve V₁ -V₄ provides animproved valve for allowing flow to occur only when a threshold pressureat the inlet of the valve has been achieved and remaining closed whenthe threshold pressure is applied as back pressure to the valve when thevalve is closed.

Since certain changes may be made in the above apparatus withoutdeparting from the scope of the invention herein involved, it isintended that all matter contained in the above description or shown inthe accompanying drawing shall be interpreted in an illustrative and notin a limiting sense.

What is claimed is:
 1. Apparatus for vaporizing a liquid into a gas,said apparatus comprising in combination:a vaporizer for vaporizing aliquid; a positive displacement pump assembly, coupled to saidvaporizer, for delivering liquid to said vaporizer at a continuous andconstant volumetric rate and pressure, said assembly comprising: firstpumping means, including a first chamber and first pump means,reciprocally operable between delivery and filling phases, fordelivering a first predetermined volume of said liquid at apredetermined rate; second pumping means, including a second chamber andsecond pump means, reciprocally operable between delivery and fillingphases, for delivering a second predetermined volume of said liquid atthe predetermined rate, wherein said first predetermined volume isgreater than said second predetermined volume by a whole number factor;first valve means for controlling the liquid provided to said firstpumping means when said first pumping means is operated in its fillingphase; second valve means for controlling the liquid delivered by saidfirst pumping means to said second pumping means during the deliveryphase of said first pumping means and the filling phase of said secondpumping means; third valve means for controlling the liquid delivered bysaid second pumping means out of said assembly to said vaporizer duringthe delivery phase of said second pumping means; and control means forcyclically operating said first and second pumping means and said first,second and third valve means as follows:(a) opening the first valvemeans and closing the second valve means, operating the second pumpingmeans in its delivery phase so as to pump liquid in the second chamberthrough the third valve means to said vaporizer, and operating the firstpumping means in its filling phase so as to fill the first chamber withliquid passing through the first valve means at a volumetric rategreater than the predetermined rate so that the first chamber is filledprior to the completion of the delivery phase of the second pumpingmeans; (b) closing the first valve means while maintaining the secondvalve means closed when the first chamber becomes filled; (c) commencingthe first pumping means in its delivery phase while maintaining thefirst and second valve means closed so that responsive to the liquid inthe first pumping means reaching a predetermined pressure (i) the secondvalve means opens while the third valve means remains open, (ii) thesecond pumping means commences its filling phase, and (iii) the firstpumping means continues operating in its delivery phase so that thevolume of liquid delivered from the first chamber to the second chamberwhile the latter is filling results in liquid passing through the thirdvalve means to said vaporizer at the predetermined volumetric rate. 2.Apparatus for vaporizing a liquid into a gas, said apparatus comprising,in combination:a vaporizer for vaporizing a liquid; and a positivedisplacement pump system, coupled to said vaporizer, for deliveringliquid to said vaporizer at a substantially continuous and constantvolumetric rate and pressure, said pump system comprising (a) first andsecond reciprocal pump means operating in combination with one anotherso that in use the first pump means fills with liquid while the secondpump means is delivering liquid to the vaporizer, and said first pumpmeans delivers liquid through the second pump means to said vaporizerwhile the second pump means is filling with liquid, and (b) valve means,including a valve connected between the first and second pump means, forcontrolling the delivery of liquid from the first pump means to thesecond pump means to insure that the liquid is at a predeterminedpressure before the liquid is delivered by the first pump means to thesecond pump means in order to insure delivery of liquid to the vaporizerat a substantially continuous and constant volumetric rate and pressure.3. Apparatus according to claim 2, wherein said vaporizer comprises:aplurality of relatively thin disks; means for supporting the disks so asto form a stack with the disks disposed parallel to and in contact witheach other; means for biasing said disks together so as to form a stack;and means for heating the disks to a temperature above the vaporizationtemperature of the liquid; wherein said pump system forces the liquidbetween the disks so that the disks separate against said biasing meansand liquid is forced through and flash vaporized in the spaces betweensaid disks.
 4. Apparatus according to claim 3, wherein said means forsupporting said disks includes liquid passage means for carrying saidliquid under pressure from the second pump means to said disks. 5.Apparatus according to claim 4, wherein said means for carrying saidliquid under pressure includes a hollow tube disposed through the centerof each disk, the tube including aperture means disposed so that liquidcarried in said tube under pressure is forced through said aperture andforces said disks apart so that the liquid is heated and vaporized inthe spaces between the disks.
 6. Apparatus according to claim 3, whereinsaid means for biasing the disks includes an anvil, and means forbiasing said anvil into contact with one end of the stack.
 7. Apparatusaccording to claim 6, wherein said means for heating said disks includesheater means for heating said disks, and said means for biasing thedisks biases the other end of the stack into thermal contact with saidheater means.
 8. Apparatus according to claim 7, wherein said means forcarrying said liquid under pressure includes a hollow tube disposedthrough the center of each disk and said heater means, the tubeincluding aperture means disposed so that liquid carried in said tubeunder pressure is forced through said heater means and said aperturemeans into said spaces.
 9. Apparatus according to claim 2, wherein saidfirst pump means fills the second pump means as said first pump meansdelivers liquid to said vaporizer, and said valve means includes atleast a first valve for controlling the liquid delivered to said firstpump means, said valve connected between said first and second pumpmeans for controlling the liquid delivered to said second pump means anda third valve for controlling the liquid delivered to said vaporizer.10. Apparatus according to claim 9, wherein each of said valves has aninlet and is constructed to open in response to fluid at its inlet at apreselected pressure and to stay closed in response to back pressureequal to said preselected pressure exerted by the fluid at its outlet.11. Apparatus according to claim 10, wherein said each of said valvescomprises:means for defining a closed passageway; means for defining aninlet to said passageway for receiving liquid up to said preselectedpressure; means for defining a fluid outlet from said passageway throughwhich liquid passes out of said valve; means for defining a valve seatwithin said passageway; a valve body movable relative to said valve seatbetween an opened position wherein the body is spaced from the seat whenthe valve is opened and a closed position wherein the body is in contactwith the seat when the valve is closed; biasing means for biasing saidvalve body into said closed position, wherein the force created by saidbiasing means on said valve body is such that the force created by saidfluid at said preselected pressure at said inlet causes said valve bodyto move to the open position when said valve body is in the closedposition, while said valve body remains in the closed position when saidfluid at said predetermined pressure is provided at said outlet when thevalve body is in the closed position.
 12. Apparatus according to claim11, wherein each valve further includes:means for providing a force onsaid valve body greater than and in the opposite direction from theforce provided by the biasing means so that said valve body can bequickly moved from the closed position to the opened position so thatliquid is immediately provided at the outlet.
 13. Apparatus according toclaim 12, wherein said means for providing the force on said valve bodyincludes a piston coupled to the valve body, said biasing means includesat least one compression spring for biasing said piston against saidvalve body so as to bias said valve body in said closed position, andmeans for receiving an actuating fluid for moving said piston againstsaid bias so as to move said valve body to said opened position. 14.Apparatus according to claim 13, wherein said actuating fluid ispressurized air.
 15. Apparatus according to claim 14, further includingmeans for sealing said passageway from said piston.
 16. Apparatusaccording to claim 15, wherein said means for sealing includes a bellowsseal.
 17. Apparatus according to claim 2, wherein each of said pumpmeans comprises:means for defining a chamber for receiving the liquid;means for defining a liquid inlet to said chamber; means for defining aliquid outlet from the chamber through which liquid passes out of saidpump means; means for defining the compartment for receiving a secondand substantially incompressible liquid; actuating means for applyingand withdrawing pressure to said incompressible liquid; wherein thecompartment and chamber are separated by means for decreasing the volumeof said chamber when said actuating means applies pressure to saidincompressible liquid so as to provide positive pressure toward saidoutlet, and increasing the volume of said chamber when said actuatingmeans withdraws pressure from said incompressible liquid so as toprovide negative pressure relative to said inlet so as to fill saidchamber.
 18. Apparatus according to claim 17, wherein said means fordecreasing and increasing the volume of said chamber includes anexpandable bellows seal separating said chamber from said compartment.19. Apparatus according to claim 18, wherein said actuating meansincludes a shaft having a uniform cross section along its length, andmeans for moving said shaft at a constant speed into and out of saidcompartment.
 20. Apparatus according to claim 19, wherein said actuatingmeans further includes a stepping motor for moving said shaft at aconstant speed into and out of said compartment.
 21. Apparatus accordingto claim 20, wherein said actuating means includes a ball nut assemblycoupling said stepper motor to said shaft.
 22. Apparatus according toclaim 2, further including transfer means for transfering liquid from asource of said liquid to said pump system, wherein each of said pumpmeans reciprocally operates between (a) a filling phase wherein the pumpmeans fills with liquid provided by said transfer means, and (b) adelivery phase wherein liquid is delivered to the vaporizer. 23.Apparatus according to claim 22, wherein each of said pump meansincludes a fluid inlet for receiving liquid during a filling phase ofthe pump means and a fluid outlet for providing fluid during thedelivery phase of the pump means, said apparatus further includingcontrol means for selectively controlling the valve means so as tocontrol the flow of liquid through each inlet and outlet of each pumpmeans.
 24. Apparatus according to claim 23, wherein said valve meansincludes a valve correspondingly coupled to each inlet and outlet ofeach pump means for independently and selectively controlling the flowof liquid through each inlet and outlet, and said control meansselectively and independently controls the opening and closing of eachvalve so that liquid is delivered by said pump system to said vaporizerat the substantially continuous and constant volumetric rate andpressure.
 25. Apparatus according to claim 22, wherein said first pumpmeans fills the second pump means as said first pump means deliversliquid to said vaporizer, and the filling phase of said first pump meansallows for a predetermined amount of excess liquid to be provided to thefirst pump means so as to allow for compressibility of said liquid. 26.Apparatus according to claim 2, wherein the vaporizer is a flashvaporizer.
 27. Apparatus according to claim 2, further including storagemeans, coupled to said pump system, for storing said liquid. 28.Apparatus according to claim 2, wherein each of the pump means isreciprocally operable between delivery and filling phases, wherein thefirst pump means is connected to deliver liquid to the second pump meanswhen said first pump means operates in its delivery phase, said firstpump means delivering a predetermined volume of liquid at a faster rateduring its delivery phase than the second pump means fills during itsfilling phase, so that the first pump means simultaneously fills thesecond pump means and delivers liquid to the vaporizer during itsdelivery phase.
 29. Apparatus according to claim 28, wherein the fasterrate of delivery of liquid by the first pump means is twice that of therate of filling of liquid provided by second pump means.
 30. Apparatusfor vaporizing a liquid into a gas, said apparatus comprising, incombination:a vaporizer for vaporizing a liquid; a positive displacementpump assembly, coupled to said vaporizer, for delivering liquid to saidvaporizer at a continuous and constant volumetric rate and pressure,said assembly comprising:first pumping means, including a first chamberand first pump means, reciprocally operable between delivery and fillingphases, for receiving liquid from a source and delivering a firstpredetermined volume of the liquid at a predetermined rate and pressure;second pumping means, including a second chamber and second pump means,reciprocally operable between delivery and filling phases, for receivingliquid from said first pumping means and delivering a secondpredetermined volume of said liquid at said constant volumetric rate andpressure, wherein said first predetermined volume is greater than saidsecond predetermined volume; control means, cyclically operating saidfirst and second pumping means, for controlling the liquid provided toand from said first and second pumping means so that(a) when the secondpump means operates in its delivery phase so as to pump fluid in thesecond chamber to the vaporizer, the first pump means operates in itsfilling phase so as to fill the first chamber with fluid from saidsource at a volumetric rate greater than the predetermined rate so thatthe chamber of the first pump means is filled prior to the completion ofthe delivery phase of the second pumping means; (b) the delivery phaseof the first pump means is commenced prior to the completion of thedelivery phase of the second pumping means so that when the secondpumping means commences its filling phase the fluid in the first pumpmeans reaches a predetermined pressure, and (c) the first pump meanscontinues operating in its delivery phase during the filling phase ofthe second pumping means so that fluid is simultaneously delivered (i)from the first pumping means to the second pumping means while thelatter is filling and (ii) at said constant rate to said vaporizer.